Chapter 4 - Las Vegas Wash Coordination Committee

Chapter 4 

Water Quality 

Introduction 

The Las Vegas Wash (Wash) is a unique ecosystem in southern Nevada. 

Rarely would one expect to find an oasis of water, wildlife and vegetation 

on the floor of a desert valley, but that is precisely what exists in the southeast 

part of the Las Vegas Valley. What makes this ecological diversity 

possible is the perennial flow of water present in the Wash. 

The Wash is the primary outlet for water flows from the metropolitan 

Las Vegas Valley (Valley). The flow in the Wash is 

defined by one of two general categories; dry weather (base 

flow) and wet weather flows. Dry weather flows consist of 

metered flows, including treated wastewater from the three 

Valley dischargers (Cities of Las Vegas and Henderson, and 

the Clark County Sanitation District), once-through cooling 

water from Timet at the Basic Management, Incorporated 

industrial facility, urban runoff, and intercepted shallow 

ground water. Wet weather flow consists of storm flow. 

The water quality in the Wash is typical of most urban waterways 

and each flow component has a unique characteristic 

that contributes to the overall water quality in the Wash. 

Table 4.1 identifies each flow component, describes how the 

flow reaches the Wash, and discusses the general water quality issues of 

concern associated with each component. Figure 4.1 spatially shows the 

various flow components of the Wash in relationship to the Valley. 

Las Vegas Wash Flow 

Components 

Dry weather flows 

4 metered flows such as treated 

wastewater & once-through 

cooling water 

4 urban runoff 

4 intercepted shallow ground 

water 

Wet weather flow 

4 stormwater 

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Chapter 4: Water Quality 

Table 4.1 - Las Vegas Wash flow components and general effect on water quality. 

The water quality issues presented by the Wash have the potential to effect 

the Las Vegas Bay and generate public concern regarding Lake Mead, 

which is the largest reservoir on the Colorado River system. Southern 

Nevada relies on the Colorado River as the primary source for drinking 

water. Others in the lower Colorado River Basin including Arizona, 

California, and several Native American Tribes rely on Colorado River 

water primarily for agriculture uses as well as drinking water. Lake Mead 

plays an integral role in regulating and protecting the delivery of water to 

those entities, and southern Nevada has a vested interest in protecting the 

lake’s water quality as much as possible. In addition, flows in the Wash 

are instrumental in sustaining wetlands and the associated ecosystems that 

have developed as a result of the perennial flow. Therefore, the water 

quality issues associated with the Wash require attention. 

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Figure 4.1 - Map showing the spatial influence of various flow components in the Las 

Vegas Wash. 

Water Quality Compliance 

Safe Drinking Water Act 

The Safe Drinking Water Act (SDWA) was passed by Congress in 1974 

and has been amended several times since, most recently in 1996. The U.S. 

Environmental Protection Agency is the lead federal agency that determines 

the regulations and provides guidance to the administering agency, 

the Nevada Bureau of Health Protection. The SDWA sets national drinking 

water standards that must be met by all public water systems. 

While the Wash is not a drinking water source and therefore not required to 

meet SDWA standards, any impact, or potential impact of the Wash on 

Lake Mead must be evaluated. 

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Clean Water Act 

The Clean Water Act (CWA) mandates that all discharges to surface waters 

be permitted and meet certain requirements as to quality. The U.S. 

Environmental Protection Agency (EPA) is the lead federal agency that 

determines the regulations and provides guidance to the administering 

agency, the Nevada Division of Environmental Protection (NDEP). The 

CWA sets national standards for surface water bodies based on uses other 

than drinking water (i.e., recreation) that must be met by all entities that 

discharge to a public waterway. 

The Wash serves as the receiving waters for three types of flows which fall 

under the jurisdiction of the CWA: 

• Wastewater discharges – National Pollutant Discharge Elimination 

System (NPDES) permits are required for all of the treated wastewater 

that is discharged into the Wash. Each permit specifies the maximum 

amount of discharge allowed and sets limits for various constituents that 

may be in the discharge. The permit’s limitations are established to 

insure that water quality standards for the Wash and Lake Mead are met. 

These standards are set by NDEP, according to CWA requirements, 

based on the intended use of the water and to prevent degradation of 

water quality. 

• Stormwater flows – The Clark County Regional Flood Control District, 

as lead agency, along with Clark County, the City of Henderson, the 

City of Las Vegas, the City of North Las Vegas, and the Nevada 

Department of Transportation are co-permittees for the Municipal 

Stormwater Management NPDES permit currently in place for the urban 

Valley. The permit allows for discharge of stormwater from Valley 

washes to the Wash. Although stormwater is not treated prior to entering 

the Wash, sampling and reporting requirements are set under the 

Municipal Stormwater Management NPDES permit. 

• Urban runoff – The Valley’s urban runoff is monitored through the 

Municipal Stormwater Management NPDES permit. Under this permit, 

dry weather and wet weather sampling and reporting are conducted at 

each of the wet weather monitoring sites. In addition, the 1998/99 program 

includes a pilot project conducted by the Conservation District of 

Southern Nevada to perform a site characterization of a four-square mile 

area along Flamingo Wash to determine the sources of urban runoff pollutants. 

Triennial Review of Water Quality Standards 

Section 303 of the CWA requires that states periodically review and, as 

appropriate, modify water quality standards. The standards are published 

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under the Nevada Water Pollution Control Regulations (NAC 445A.194 – 

445A.201). The Nevada Division of Environmental Protection, Bureau of 

Water Quality Planning is the lead state agency. One important consideration 

is that beneficial uses and associated water quality standards on the 

Wash may need to be revisited as the management plan is implemented and 

as the Wash changes from a fast-moving erosive stream to a controlled 

wetland environment. 

The Nevada State Environmental Commission, which is responsible for the 

final approval, first enacted water quality standards for the Wash and Lake 

Mead in the 1970’s. The standards have been amended several times, 

including most recently in June, 1998. 

208 Water Quality Management Plan 

The Clark County 208 Water Quality Management Plan for the Valley was 

amended by County Commissioners in 1997. The document outlines water 

quality strategies for compliance under the CWA for a twenty year period. 

Elements considered in the plan include population projections, water 

resources, air quality relating to assessment of wastewater conditions, nonpoint 

source conditions, Wash wetlands, and reuse and reclamation opportunities. 

The document is subject to approval by NDEP and EPA. 

Water Quality Issues of Concern 

The fact that the Wash is the outlet for all urban flow in the Valley inherently 

means that there will be water quality issues associated with the flow. 

The primary issues of concern, including sediment, selenium, perchlorate, 

and urban chemicals are discussed in more detail below. 

Sediment 

Sediment transport in the Wash ranges from 50 to 1,600 tons per day, as 

measured by total suspended solids (TSS). As expected, the variation in 

sediment load depends upon the time the samples were collected (i.e., 

higher TSS values when sampled during or immediately after a storm 

event). Another component of the sediment equation, which cannot be 

directly measured, is sediment that drops out at Lake Las Vegas. Lake Las 

Vegas is a constructed lake that allows the Wash to flow underneath in two 

84-inch pipes. Sediment drops out in the settling basin before the flow 

enters the pipe intake structure. 

The transport of sediment is especially evident in Las Vegas Bay, the 

receiving water body of the Wash. Some researchers have noted several 

additional feet of sedimentation in the Bay after major storm events. 

On June 17, 1998, the Nevada State Environmental Commission adopted 

Water Quality Standards (NAC 445A.195) which included a beneficial use 

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Chapter 4: Water Quality


TMDL (total maximum 

daily load) 

establishes limits 

on the total mass of 

a water quality 

parameter that is 

allowed to be 

discharged into a 

water body. 

standard for suspended solids of 135 milligrams per liter (mg/l). The standard 

is defined as the twelve month rolling average of the monthly values 

and does not apply when flow in the Wash is greater than 110% of average 

flow as measured at the nearest flow gage. Based on data collected by the 

Lake Mead Water Quality Forum Sedimentation Subcommittee and by the 

Dischargers for their discharge permits, the Wash has occasionally exceeded 

the 135 mg/l total suspended solids standard. 

TMDLs 

NPDES permits issued in the Valley include regional total maximum daily 

load (TMDLs) and wasteload allocations for phosphorus and ammonia 

nitrogen. TMDL is an estimate of the assimilation capacity of a body of 

water for a particular contaminant. Wasteload allocations are the mass limits 

of a contaminant allocated to individual treatment plants such that the 

total mass for all plants does not exceed the established TMDL. The 

objective of TMDLs is to establish limits on total mass of these nutrients 

entering Lake Mead via the Wash from all sources rather than establishing 

concentration limits for individual treatment plants. 

In 1989, the NDEP established TMDLs for phosphorus (434 pounds per 

day) and ammonia (970 pounds per day). These TMDLs are divided into 

wasteload allocations among the Dischargers with a portion of the phosphorus 

TMDL (100 pounds per day) allocated to non-point sources. The 

phosphorus TMDL is in effect from March 1st through October 31st of 

each year. The ammonia TMDL is in effect from April 1st through 

September 30th of each year. 

The established TMDLs do not change as a result of increasing wastewater 

flow. Therefore, treatment technology must be improved to meet the 

TMDLs. The challenge faced by the Dischargers is developing and implementing 

the technology necessary to meet the TMDL standards as the 

amount of wastewater inflow continues to increase. 

In 1997, the Dischargers commissioned the Wastewater Needs Assessment 

Study (NAS) (Appendix 8.1). The goal of the NAS was to develop a thirty-year 

plan that addresses the long-term needs of the Dischargers and to 

identify alternative methods to accommodate the existing and projected 

wastewater flows of the Valley. Recently, the Dischargers governing bodies 

approved the implementation of the Alternative Discharge Study 

(Project). The current Project is a recommendation of the NAS effort by 

the Dischargers and is intended to expand the findings of the NAS with the 

intent to provide guidance on the engineering, scientific, and environmental 

solutions for disposal of treated wastewater in a manner that will be 

acceptable to the Dischargers and the other stakeholders. 

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Selenium 

While background selenium concentrations throughout the Colorado River 

System and Wash are one to three parts per billion (ppb), concentrations 

from one urban tributary (Monson Channel) to the Wash have been most 

recently sampled at 15 ppb. A concentration at this level raises concerns 

regarding the potential for bioaccumulation within the food chain and may 

be related to adverse effects on some species of fish and wildlife found in 

areas with elevated selenium concentrations (e.g., Kesterson). 

These elevated selenium concentrations occur in the area of the future 

entrance to the Clark County Wetlands Park. In order to assess, and eventually 

mitigate this concern, Clark County is working with the Bureau of 

Reclamation and Ducks Unlimited to design the constructed wetlands in 

this area with the idea of blending the Monson Channel water with other 

sources including effluent and Wash flows. 

While it is not anticipated that concerns regarding selenium will delay the 

enhancement activities planned for the Wash, it is important to better 

understand the effects of selenium within the ecosystem. One way to do 

this is by developing a demonstration project that will effectively assess the 

selenium cycle. 

Perchlorate 

Perchlorate, detected in the Wash and Lake Mead in 1997, was manufactured 

by two Valley companies from the 1950’s until 1997. Advancement 

in technology has lowered the detection limit for perchlorate from 400 ppb 

to four ppb and has resulted in perchlorate being detected at low levels 

(less than 18 ppb) in the raw and finished drinking water supply from Lake 

Mead. NDEP has determined that the source of perchlorate in Lake Mead 

is intercepted shallow ground water in the Wash. High levels of perchlorate 

have been discovered in shallow ground water surrounding and down 

gradient from the two companies that manufactured perchlorate in the 

Valley. High levels have also been detected along the stretch of the Wash 

where intercepted shallow ground water enters the Wash. Figure 4.2 shows 

the location of the perchlorate plume extending from the source of contamination 

at the industrial facilities to the Wash. 

For the data that has been collected in the Wash and Lake Mead, the values 

of perchlorate vary from about 10-20 ppb to about 1,000 ppb depending 

upon where the samples were collected. For example, the values above the 

point where the perchlorate plume enters the Wash range from 10-20 ppb. 

In the area the perchlorate plume intercepts the Wash, the perchlorate value 

increases to about 1,000 ppb. The values decrease dramatically once the 

Wash enters Las Vegas Bay due to dilution from the large volume of water 

in the Bay. Figure 4.2 shows the perchlorate values throughout the Wash, 

Las Vegas Bay, and the Boulder Basin of Lake Mead. 

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Figure 4.2 - Perchlorate values in Las Vegas Wash, Las Vegas Bay and the Boulder Basin of Lake Mead. 

The NDEP has been actively working with the responsible parties to facilitate 

the removal of perchlorate from the shallow ground water system, 

which will result in a decrease of values seen in the Wash and Lake Mead. 

One recent discovery was the presence of a shallow ground water seep of 

about 350 gallons per minute that, based on mass balance calculations, is 

estimated to contribute about fifty percent of the total perchlorate load into 

the Wash. The NDEP has required the responsible parties to focus on this 

site by intercepting the flow and removing the perchlorate before it reaches 

the Wash. 

The Southern Nevada Water Authority, the NDEP, and the U.S. Bureau of 

Reclamation (USBR) have conducted water quality sampling on a monthly 

basis at over twenty locations in the Wash and Lake Mead. The fact that 

perchlorate is a conservative compound has allowed researchers to use the 

concentrations detected to better understand the limnological aspects of the 

lake, and make predictions in order to anticipate the concentrations seen in 

the raw and finished water supply. In addition, these entities promote the 

further understanding of the potential health effects of perchlorate, and will 

continue to sample, characterize, and stay informed as to the most recent 

research regarding perchlorate. 

Urban Chemicals 

The category of water quality concerns known as “urban chemicals” is a 

broad topic that covers any type of chemical that is used in the home or 

business. This category includes not only those chemicals that have been 

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disposed of improperly (i.e., on the ground, in the storm drain system), but 

also includes the chemicals prevalent in every day life. For example, pesticides, 

solvents, herbicides, gas products, oil, and grease all fall within this 

category. These chemicals have the potential to reach the Wash as intercepted 

shallow ground water or as surface flow resulting from overirrigation 

and storm events. 

The U.S. Geological Survey, as part of the National Water-Quality 

Assessment (NAWQA) Program, has collected and analyzed water quality 

samples from various shallow ground water (not used for drinking water) 

monitoring wells in the Valley. The report states that at least one pesticide 

was detected at low levels (below the maximum contaminant level established 

for drinking water) in 28 percent of the shallow monitoring wells 

sampled. The report concludes that urban activities in the Valley have 

been a primary source of these organic compounds found in the shallow 

aquifer (Bevans, et al, 1998). 

Public education and the development of Best Management Practices can 

be a successful means of reducing urban pollutants from reaching water 

ways. 

Other Potential Concerns 

The lowering of analytical detection limits, combined with a better understanding 

of flow contribution to the Wash, has led researchers to realize 

that additional water quality concerns have the potential to materialize in 

the future. Two general concerns include past industrial practices and current 

land use practices. Each of these is discussed in more detail below: 

• Past industrial practices – Prior to environmental law in the 1970’s, it 

was standard practice to dispose of manufacturing byproducts in unlined 

landfills and lagoons. Many of these past industrial practices took place 

in the southeast part of the Valley, and as a result, many of these 

byproducts have reached the shallow ground water aquifer, which then 

can reach the Wash as intercepted ground water. As discussed in more 

detail in Chapter 7, and in previous discussions in this chapter, perchlorate 

and various organic compounds are examples of past land use practices 

effecting water quality in the Wash. 

• Current land use practices - Current land use practices contribute to 

water quality in the Wash primarily as a result of dewatering and nonpoint 

sources resulting from an increasing amount of imprevious surface 

in the Valley and the associated increased runoff associated with it. 

Chapter 11 provides specific land use recommendations. 


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Understanding the Influence of Las Vegas 

Wash on Lake Mead 

Gaining the knowledge to develop and implement the management options 

that are presented in this document begins with fully understanding the 

water quality of the Wash and it’s influence on the water quality of Las 

Vegas Bay and Lake Mead. 

Water Quality Monitoring 

There are currently several monitoring programs in place that have provided 

a significant understanding of the water quality concerns faced by 

southern Nevada. The following describes some of these efforts: 

• Las Vegas Valley Dischargers – Through a program that includes water 

quality sampling for compliance and research purposes, the Dischargers 

have provided a comprehensive set of data on a wide variety of water 

quality parameters. This data is available for the Wash, Las Vegas Bay, 

and Lake Mead. 

• U.S. Bureau of Reclamation – Work by USBR researchers throughout 

the 1990’s has helped us understand the limnology of Lake Mead and 

the seasonal effects of the Wash on the ecology of Boulder Basin. 

Figure 4.3 indicates the location of the Boulder Basin in Lake Mead. 

Their work has four objectives: 

1. To collect trend data on the influence of the Wash on Las 

Vegas Bay and Lake Mead. 

2. To investigate the status of the limnological conditions of 

Boulder Basin as a source of drinking water supply. 

3. To perform research into new technology of evaluating limnological 

features, in particular those related to water quality conditions 

of reservoirs. 

4. To contribute to the understanding the ecology of Lake Mead as 

it relates to the operational scheme of the Colorado River system. 

A variety of water quality parameters are collected, including temperature, 

dissolved oxygen, conductivity, pH, turbidity, transparency, plant nutrients, 

some specific inorganic chemicals, bacteria, as well as parameters that estimate 

the algal and microscopic animal biomass of Boulder Basin. The 

results of nearly a decade of sampling has lead to increased understanding 

of the interaction of the Wash and Lake Mead. Parameters such as conductivity 

(high Wash values compared with lower Colorado River values) provide 

a signature of the Wash that can be traced from the Wash and followed 

as it mixes within the lake. The research has shown that how the 

Wash behaves once it reaches the lake is dependent on several factors 

84


including time of 

year, water temperature, 

and wind. 

As Wash water enters 

the lake and forms an 

intrusion (or plume) 

there is significant 

mixing in the inner 

bay as indicated by its 

higher overall conductivity 

versus that 

of the outer bay. 

However, the intrusion 

retains its identity 

and exists as an 

underflow for about 4 

kilometers (km) into 

Boulder Basin. This 

underflow follows the 

thalweg of the historical 

stream channel of Las Vegas Creek (now referred to as Las Vegas 

Wash) until an equilibrium depth is reached below which lake water, due to 

cooler temperatures, is denser than intrusion water. This occurs at a depth 

of 40 to 60 meters (m) in late winter. At this depth, the intrusion extends 

into the basin as an interflow, being supported by the denser water of the 

hypolimnion, until it has dispersed and mixed to the point it can no longer 

be detected using standard measurements. 

Figure 4.3 – Map of Lake Mead highlighting the location of the Boulder Basin. 

In early spring, the intrusion begins to elevate into the water column, existing 

as an underflow for a shorter and shorter distance before becoming an 

interflow. This change is a function of both stratification developing in the 

reservoir and the warming of inflowing water from the Wash. The Wash 

conductivity remains relatively stable throughout the year, but the temperature 

increases from 20° C to nearly 28° C by mid-summer. Although the 

Las Vegas Wash water is warmer than lake water, it remains underflow due 

to higher density resulting from salinity. This density gradient is strong 

enough in both late spring and early fall that water temperature of the 

intrusion may be 1-2°C higher than that of surface waters for a distance of 

2-3 km. 

By early summer, the intrusion is located at its shallowest depth of the 

year as a result of increasing temperature of the inflow and the relatively 

shallow thermocline in Las Vegas Bay. As the thermocline strengthens, 

the intrusion is constrained from below by denser cold water, and upward 

movement is limited by the less dense, warm surface waters which inhibit 

mixing. Conductivity gradients identifying the intrusion are sharpest at 

Thalweg refers to the 

location of any cross 

section of a reservoir 

where the old river, 

creek or wash 

channel was located 

before the reservoir 

was filled. It is then 

the deepest spot of 

any particular 

cross section. 

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this time. Depending on conditions, remnants of the intrusion can be 

measured for at least 8 km from the inflow of the Wash, and on occasion 

data indicate a band of higher conductivity extending to Hoover Dam. 

During most of the summer months the peak of the intrusion remains at 

about 9 meters in depth. 

At the end of summer (usually September) the intrusion sinks as the thermocline 

is depressed due to epilimnetic cooling. As stratification breaks 

down in the fall and the inflowing waters begin to cool, the intrusion 

moves deeper into the former hypolimnetic waters, and the seasonal cycle 

begins to repeat. 

Related and very recent investigations by USBR scientists indicate that the 

Wash enters and flows as a plume at an estimated average rate of 5 to 8 

centimeters per second, and that the average time it takes water flowing in 

the “plume” to travel from the Wash inflow to a point near Saddle Islands 

is 48.5 hours. 

USBR scientists, for more than 12 years, have continuously monitored 

water quality of the Wash from just above the City of Las Vegas treatment 

facility to a point below the North Shore Road bridge. Prior to the ongoing 

program, monitoring was done on a frequent basis for more than 10 years. 

These data, which continue to be collected on a quarterly basis, are done 

under the authority of the Colorado River Basin Salinity Control Act of 

1974. Data clearly depict the dramatic change in the patterns of water 

quality based upon, 1) the erosion of the Wash and resulting significant 

reduction in time of travel in the Wash, 2) the effects of increasing population, 

3) changes installed in treatment of effluent by the dischargers (i.e. 

removal of phosphorus, conversion of nitrogen from ammonia to nitrate) 

and 4) the influence of periodic flooding. 

• Southern Nevada Water Authority (SNWA) – The SNWA conducts 

water quality monitoring for compliance and research purposes. Longterm 

sampling has resulted in water quality data that dates back to the 

1970’s. Since 1997, a comprehensive sampling program has been 

underway throughout the Boulder Basin that collects water samples 

from the lake surface to lake bottom. This data will be used in a threedimensional 

model to help researchers better understand the limnology 

of the Boulder Basin and the influence of the Wash on the entire basin. 

The SNWA has also coordinated and developed a water quality database 

that provides for the centralization of data from several entities into an 

internet-based application that contains more than 500,000 cells of data. 

• Municipal Stormwater Quality Management Program - The Las 

Vegas Valley Stormwater Quality Management Committee, of which the 

Clark County Regional Flood Control District is the lead agency, pro- 

86

vides a report each year detailing the findings of monitoring and sampling 

efforts required under the Las Vegas Valley NPDES Municipal 

Stormwater Discharge Permit. The current Annual Report (1997-1998) 

outlines program requirements, recommended changes for the following 

permit year, and water quality data collected for the year. The monitoring 

under this program began in 1991. 

Interagency Coordination 

Over the past several years, entities involved in water quality issues for 

southern Nevada realized that a coordinated effort was the preferred 

method to share information and identify needs for the future. In addition 

to the Coordination Committee, other efforts are underway to ensure that 

the water quality issues facing the Valley are identified and addressed. 

• Water Quality Database – The Las Vegas Water Quality Interagency 

Database (www.lvwaterquality.org) is an example of using state-of-the 

art technology to manage and access large data sets. This internet-based 

application has helped to centralize water quality data from federal, 

state, and local entities, while at the same time, providing the public 

with an easy-to-use tool to understand water quality data in our community. 

The site consists of two sections, one for water quality professionals 

who can query large datasets and obtain results in an easy to read, 

downloadable fashion within a few seconds. The second section is 

designed with the general public in mind and focuses on education 

while enabling the public to query the water quality database and graph 

the results. The database is intended to be used as a research tool and 

an educational outreach mechanism for the local community. The database 

was developed, and is currently maintained by the Las Vegas Wash 

Project Coordination Team. The site currently includes data from the 

Bureau of Reclamation, City of Henderson, City of Las Vegas, Clark 

County Regional Flood Control District, Clark County Sanitation 

District, and the Southern Nevada Water Authority. 

• Lake Mead Water Quality Forum (Forum) – The Forum was established 

in 1997 and is facilitated by the Nevada Division of 

Environmental Protection. The Forum is comprised of local, state, and 

federal agencies with an interest in Lake Mead environmental issues and 

water quality. The purpose of this group is to provide a mechanism to 

keep the stakeholders of the Wash and Lake Mead informed as to the 

water quality issues and ongoing studies. The Forum has also initiated 

several technical studies that investigated topics such as, sediment volume 

from the Wash, whether there was a need for a fish consumption 

advisory, and the potential for bacteria after a storm event to impact designated 

water uses on Lake Mead. 


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• Interagency Technical Committee – This group meets monthly on 

issues related to Lake Mead and the Wash monitoring activities. Studies 

are conducted to improve and standardize sampling and analytical procedures 

and to insure reliability of data generated by all participants. 

This group has taken on the formidable task of developing a common 

nomenclature for the 100+ sampling locations throughout the Lake 

Mead system. The participants of this group include representatives 

from the Bureau of Reclamation, City of Henderson, City of Las Vegas, 

Clark County Sanitation, and the Southern Nevada Water Authority. 

Characterization of Las Vegas Wash 

Water Quality 

The overall water quality in the Wash is clearly dependent upon the quality 

of the individual flow components. For example, the quality of Wash 

water, when looked at without the contribution of the treated wastewater 

(effluent), is typical of an urban area; high in total dissolved solids and 

containing low levels of oil, grease, pesticides, and herbicides (Clark 

County Regional Flood Control Stormwater Monitoring Program). Once 

the effluent component is added, the values decrease due to the dilution 

effect of the large volumes of effluent, and more closely resemble 

Colorado River water. 

The water quality parameter that best demonstrates the dilution effect that 

occurs once the treated wastewater flow enters the Wash is total dissolved 

solids (TDS). Table 4.2 shows the TDS values of four sample locations; 

two sites without the influence of effluent and two sites downstream from 

the treated wastewater entering the Wash. Figure 4.4 locates the samples 

sites presented in Table 4.2. 

Table 4.2 - Total dissolved solids values with and without influence of effluent contribution (from 

www.lvwaterquality.org/agency). 

Understanding the individual flow components and their effect on the overall 

water quality in the Wash will aid researchers in developing and implementing 

the various elements of the Las Vegas Wash Comprehensive 

Adaptive Management Plan. 

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Figure 4.4 – Sample sites indicating influence of urban run-off, shallow ground 

water, and treated wastewater. 

Summary 

The work being done through the interagency coordination efforts in the 

Valley, including the Lake Mead Water Quality Forum, the Interagency 

Technical Committee, and the Las Vegas Wash Coordination Committee, 

have provided us with an opportunity to better understand the effects of 

urban flows on the Wash and Lake Mead. Through this understanding has 

come the realization that the Wash water quality concerns we face as a 

community effect not only southern Nevada, but also the downstream users 

of the Colorado River, and that a comprehensive approach to mitigating the 

concerns and managing the resource is necessary. 

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Chapter 4 - Las Vegas Wash Coordination Committee

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